Generally, a parking assistance system of a vehicle overlaps a guide line image for reverse parking with a rearward image of the vehicle that has been captured by a rear camera, and displays the rearward image with the guide line image overlapped therewith, thereby providing a driver's convenience in reverse parking. As an example of such a technology, Korea Patent Publication No. 10-2011-0056593 has been disclosed a parking guide system. The parking guide system includes a steering angle measurement module, an image capture module, an image processing module, and a display module. The steering angle measurement module measures the steering angle information of a handle, and the image capture module captures a rearward region of a vehicle. The image processing module generates an overlap image by overlapping an image, captured by the image capture module, with a steering linkage trace line based on steering angle information that has been measured by the steering angle measurement module. The display module displays the image generated by the image processing module. As described above, a related art parking guide system displays a steering linkage trace line that is based on the rotation of a handle in reverse parking, and thus assists the reverse parking that is performed by a driver. However, when a parking space is very dark, it is difficult to visually check the parking space even though an image captured by a rear camera of a vehicle is displayed. In this case, the related art parking guide system cannot properly assist reverse parking that is performed by a driver.